CASE STUDY
National Renewable Energy Laboratory
Testing Wind Turbine Power Generators using PULSE
United States of America
Industrial Products
PULSE
The National Renewable Energy Laboratory (NREL) is operated for the U.S. Department of Energy by the
Midwest Research Institute, Battelle, and Bechtel. Within NREL is the National Wind Technology Center
that carries out advanced research on all aspects of wind turbine power generation and provides support
to the American wind turbine industry.
Wind turbine noise is an important environmental issue, not only in the U.S. but throughout the world.
The National Wind Technology Center uses a PULSE™ system to measure the noise produced by wind
turbines and their component parts. The test data is used in the design and development of wind turbine
generator systems and to ensure that the noise produced by a design is within the specified levels.
History
The National Renewable Energy Laboratory, founded 25 years ago, is operated for the U.S. Government’s
Department of Energy by the Midwest Research Institute, Battelle, and Bechtel. Within NREL, the National
Wind Technology Center carries out state-of-the-art research into all aspects of wind turbine generators and
their components. It provides extensive support to the wind turbine industry, not only in the U.S. but
throughout the world.
The National Wind Technology Center, established ten years ago, is located at Golden, some 20 miles (32 km)
northwest of Denver, Colorado and in the midst of spectacular scenery. The flat countryside, flanked by a
range of mountains to the west that reach up to more than 12 000 feet (3650 m), provides near perfect
conditions for testing wind turbine generators with constant wind-speeds that vary from hurricane force
down to still-air conditions.
Research & Development
The laboratories at Golden extend to some 6000 square feet (557 m2). The research
carried out covers many areas and includes the latest aerodynamic research into the
performance of turbine blades, the design of major components used in the construction
of wind turbines, their efficient siting, and a range of environmental issues that especially
focus on wind turbine noise. Investigations extend to the affects of wind turbines on
wild-life and the problems of bird-strikes.
The current total power produced by wind turbines throughout the U.S. is about 4400
megawatts. The wind turbine industry is expanding rapidly, not only in America but
throughout the world and a number of large companies dominate the market and
operate internationally.
Although funded by the U.S. Government, in addition to providing support to the
industry, the National Wind Technology Center also operates as a consultant organisation and carries out specific research and testing for many companies that manufacture
components and complete wind turbine power generation systems.
Engineering Expertise
Fig. 1
Arlinda A. Huskey
has worked at the
National Wind
Technology Center
for eight years. She
has extensive wind
turbine experience
and sat on the
committee that
established the
latest IEC Standard
The National Wind Technology Center has about one hundred employees and it has assembled a group of engineers
with extensive experience and expertise in the design of
wind turbines.
Arlinda A. Huskey has worked at Golden for eight years. Arlinda has a B.Sc. in Mechanical Engineering from Arizona
State University and is currently studying for her Masters’,
also in Mechanical Engineering at The University of Colorado.
Jeroen J.D. van Dam is a Dutchman. He has a Master’s
degree in aerospace engineering from Delft University in
The Netherlands. Before joining the National Wind Technology Center two years ago, Jeroen worked at The Netherlands Energy Research Foundation for five years.
Fig. 2
Jeroen J.D. van
Dam has a Master’s
degree in
aerospace
engineering. He
also sat on the IEC
Standard
committee
Design Compromise
Arlinda explains, “There are many variable factors in the
design of a modern wind turbine. Some configurations provide optimum power while others give the highest efficiency or produce the lowest noise. There are two major
schools of thought. One favours the use of a two-blade
turbine that runs downwind while the other prefer a threeblade design that faces into the wind”.
In general, three blade turbines are considered to be quieter
than those with two blades since they normally rotate slower.
2
Turbine Noise
Fig. 3
This 600 kW wind
turbine at NREL’s
facility is used to
investigate the
noise produced by
typical downwind
two-blade designs
Arlinda says, “The noise produced by wind turbines is a major factor in Europe, and it’s becoming an increasingly important issue a not only in
the U.S. but throughout the world. Much of our
investigative work is in this area and it occupies
about 50% of my time.”
Jeroen continues, “We carry out a lot of research
on components with a view to decrease the cost
of energy of wind turbines and to reduce their
environmental impact. Most blades are currently
made of glass fibre but there is currently a transition to carbon fibre with the advantages of a
much higher strength to weight ratio and lower
total weight. We experiment with both fixed and
variable pitch blades and with turbines of different
sizes. The critical factor is the power curve of the
design – the power output compared to the wind
speed.”
Jeroen adds, “Some wind turbines are very large. The blades rotate at about 30 rpm
and the blade tips can reach a speed of 60 meters per second. The slower the blade,
the less noise but this affects the power output so, as Arlinda mentioned, there are
many factors that must be considered.
PULSE
Fig. 4
A threeblade100 kW
turbine generator
at NREL’s facility.
This configuration
runs into wind and
tends to be quieter
than designs using
two blades
The National Wind Technology Center recently
purchased a 6/1-channel Portable PULSE system
for general NVH analysis and investigations into
turbine noise with respect to noise legislation.
Before the acquisition of PULSE, noise data was
stored on a DAT recorder and post-processing
analysis was subsequently carried out in the laboratory.
With PULSE, analyses can be made in real time
on a laptop PC and the complete portability of
the system enables it to be easily transported to
other sites around the world. The DAT recorder
is no longer necessary and post-processing of the
data can be performed anywhere, and at any
time.
If, in the future, the National Wind Technology
Center’s testing demands grow, then PULSE can
be easily expanded to provide more functionality,
and this was another key reason for selecting it.
3
Testing
Fig. 5
The National Wind
technology Center
at Golden has been
established for 10
years. The site
provides nearperfect testing
conditions – and
there are not many
neighbours!
To determine the noise characteristic of a turbine, it is necessary to place the microphones at
a number of different positions and to also measure the main operating parameters.
Four microphones are normally used, and are
positioned around the turbine. The positions of
the microphones are determined by the tower
height and blade diameter. The data from the
microphones can be analysed in real-time and is
also stored in PULSE for post-processing analysis.
Other factors such as the wind direction, wind speed and the turbine power output are
also measured and stored in PULSE. The noise response is typically measured over a
frequency range from 20 Hz to 10 kHz.
Arlinda explains, “Because a noise test depends on the wind blowing from the right
direction and at a correct speed, a typical test could last from just a few hours up to
more than a week.”
The microphones are calibrated using a Brüel & Kjær Calibrator Type 4231 before each
testing session, or at intervals of every two hours, whichever is less.
Jeroen adds, “The noise measurements must be taken with both the turbine running
and when parked so that the background noise can be measured. We must make sure
that there is no ‘external’ noise present during the measurement process. This includes
trains, planes, dogs barking, etc. We once had a problem with a field full of goats close
to a turbine! It’s therefore vital that we can listen to the noise recorded by the system
as the measurements are made”.
IEC Measurement Standard
Fig. 6
Standard pattern
for microphone
measurements
positions (plan
view) in the draft
IEC Standard
61400 – 11
4
Many countries around the world have enacted legislation that sets the levels of noise
allowed for wind turbine generators. Typical
values are an SPL of 40 dB (A) during the day
and 35 dB (A) at night.
A new IEC Standard 61400 – 11 edition 2 is in
its final draft stage, and when ratified, will
specify the techniques for the acoustic noise
measurement of wind turbine generator systems. The second edition draft specifies one
microphone with three others as optional.
The first edition specifies four microphones.
In both editions, the reference microphone
position is always required. One microphone
is placed immediately downwind of the turbine, two are placed at 60 degrees from the
turbine centre line and downwind of it, and
a fourth is placed on the center-line at the
back (upwind) of the turbine.
The draft IEC standard specifies all parameters relevant to the measurement of turbine
noise including:
❍
❍
❍
❍
Instrumentation – acoustic and non-acoustic instruments, traceable calibration
Measurements and measurement procedures – measurement positions, acoustic and
non-acoustic measurements
Data reduction procedures
− Wind speed
− Correction for background noise
− Apparent sound power (A-weighted)
− 1/3-octave (CPB) levels
− Tonality (using FFT analysis)
− Directivity (optional) – how much the noise varies with the wind direction
Information to be reported – characterisation of the wind turbine, physical
environment, instrumentation, acoustic and non-acoustic data, uncertainty
Arlinda and Jeroen were members of the IEC committee that drafted the new standard.
Arlinda represented the U.S.A. and Jeroen represented The Netherlands.
Data and Reporting
Test data is held on the laptop PC’s hard disk and archived on CD-ROM. Reports are
made using the PULSE export facility to the Microsoft® Office suite and then created
in Word and Excel. It’s easy, quick and effective.Data from a previous test can be easily
accessed and compared.
❍
❍
❍
❍
❍
❍
❍
❍
❍
❍
The National Renewable Energy Laboratory is operated for the U.S. Department of
Energy by the Midwest Research Institute, Battelle, and Bechtel
Within NREL, the National Wind Technology Center carries out advanced research
on all aspects of wind turbine power generation
The current total power produced by wind turbines throughout the U.S. is about
4400 megawatts
The National Wind Technology Center supports the U.S. wind turbine industry, and
also operates as a consultancy
“The noise produced by wind turbines is a major factor in Europe, and it’s becoming
an increasingly important issue not only in the U.S. but throughout the world”
The National Wind Technology Center recently purchased a 6/1-channel PULSE system
for general NVH analysis and investigations into turbine noise with respect to noise
legislation
PULSE enables analyses to be made in real time on a laptop PC – the portability of
the system enables it to be easily transported to sites around the world
If testing demands grow, PULSE can be easily expanded to provide more functionality
Microphones are calibrated using a Brüel & Kjær Calibrator Type 4231
IEC Standard 61400 – 11 specifies the techniques for the acoustic noise measurement
of wind turbine generator systems
Reports are made using the PULSE export facility to the Microsoft® Office suite
HEADQUARTERS: DK-2850 Nærum · Denmark · Telephone: +45 4580 0500 · Fax: +45 4580 1405 · bksv.com · e-mail: info@bksv.com
Australia (02)9889-8888 · Austria 0043-1-8657400 · Brazil (011)5188-8166 · Canada (514)695-8225 · China (86) 1068029906
Czech Republic 02-67021100 · Finland (0)9-755 950 · France (01)69907100 · Germany 421 17 87 0 · Hong Kong 25487486 · Hungary (1)2158305
Ireland (01)803 7600 · Italy 02 57 68061 · Japan 03-3779-8671 · Republic of Korea (02)3473-0605 · Netherlands (31)318 559290 · Norway 66771155
Poland (22)816 7556 · Portugal (1)4711453 · Singapore (65) 377- 4512 · Slovak Republic 421 2 5443 0701 · Spain (91)6590820 · Sweden (08)4498600
Switzerland (0)1 880 70 35 · Taiwan (02)7139303 · United Kingdom (0)1438 739 000 · USA 800 332 2040
Local representatives and service organisations worldwide
BO 1951 − 11
❍
03/03
Key Facts